Use of catalyst composition for cementing a wellbore and cement slurry for the same

ABSTRACT

The present invention relates the use of acatalyst composition consisting of ammonium chloride, aluminum chloride, and magnesium oxide for addition to cement for oil well cementing. Moreover, the invention relates to a method of cementing a wellbore, comprising the steps of: i) drilling a wellbore; ii) introducing a casing string into the wellbore; iii) preparing a cement slurry based on a combination of cement and a catalyst composition consisting of ammonium chloride, aluminum chloride, and magnesium oxide; iv) pumping said cement slurry into the wellbore; and v) allowing said cement slurry to set. In addition, the invention relates to a cement slurry for cementing a wellbore, comprising i) cement, ii) water; and iii) a catalyst composition consisting of ammonium chloride, aluminum chloride, and magnesium oxide.

BACKGROUND

The present invention relates to a catalyst composition for use incementing a wellbore, a method for cementing a wellbore and to a cementslurry.

Patent EP 1 349 819 (corresponding to U.S. Pat. No. 7,316,744) of thepresent inventor discloses a composition for reinforcing cement, whichcontains: a) sodium chloride, potassium chloride, magnesium chloride,calcium chloride, strontium chloride, barium chloride and/or ammoniumchloride; b) aluminum chloride; and c) silica and/or zeolite and/orapatite. EP 1 349 819 is incorporated by reference in its entirety.

This composition for reinforcing cement according to EP 1 349 819 iscommercially available from PowerCem Technologies B.V. under theregistered trade names of PowerCem and RoadCem.

In U.S. patent applications of the present inventor U.S. Ser. No.13/654,920 and U.S. Ser. No. 13/540,181 the use of said composition forreinforcing cement according to EP 1 349 819 for cementing wellbores isdisclosed.

It is an aim of the present invention to provide an alternative cementslurry using a more reactive, catalytic composition.

SUMMARY OF THE INVENTION

This aim is obtained by the use of a catalyst composition consisting ofI) ammonium chloride, II) aluminum chloride, and III) magnesium oxidefor addition to cement for oil well cementing.

In other words, the present invention relates to a method of cementing awellbore, comprising the steps of: i) drilling a wellbore; ii)introducing a casing string into the wellbore; iii) preparing a cementslurry based on a combination of cement and a catalyst compositionconsisting of I) ammonium chloride, II) aluminum chloride, and III)magnesium oxide; iv) pumping said cement slurry into the wellbore; andv) allowing said cement slurry to set.

Moreover, the invention relates to a cement slurry for cementing awellbore, comprising i) cement, ii) water; and iii) a catalystcomposition consisting of I) ammonium chloride, II) aluminum chloride,and III) magnesium oxide.

In an embodiment, said cement slurry comprises between 50 and 85 wt %,preferably between 65 and 75 wt % of I) cement, and between 20 and 40 wt%, preferably between 25 and 30 wt % of II) water, and between 0.1 and10 wt %, preferably between 1 and 3 wt %, more preferably between 1.5and 2.5 wt % of catalyst composition III).

In an embodiment, the total quantity of components from group I) may be1 to 25% by weight, preferably 5 to 15% by weight, more preferably 8 to13% by weight; most preferably 10 wt. % based on the total weight ofI)+II)+III).

In an embodiment, the total quantity of components from group II) may be10 to 50% by weight, preferably 20 to 40% by weight, more preferably 25to 35% by weight, most preferably 30 wt. % based on the total weight ofI)+II)+III).

In an embodiment, the total quantity of components from group III) maybe 5 to 40% by weight, preferably 10 to 30% by weight, more preferably15 to 25% by weight, most preferably 20 wt. % based on the total weightof I)+II)+III).

DETAILED DESCRIPTION OF THE INVENTION

Extensive studies by the present inventor have revealed that with theuse of the composition of EP 1 349 819 (viz. comprising sodium chloride,potassium chloride, ammonium chloride, magnesium chloride, calciumchloride, aluminum chloride, silica, magnesium oxide, magnesium hydrogenphosphate, magnesium sulfate, sodium carbonate, and cement) a certaincombination of specific components are responsible for the activation ofthe remaining components. The present catalytic composition comprisesthese specific components and imposes reactivity on the other componentsto a full oxidation reaction when water is added to the dry mixture.

Based on this remarkable and surprising finding, the inventor hasarrived at the present invention.

Without wishing to be bound by a theory, the following is observed.Several of the components of the RoadCem or PowerCem product of EP 1 349819 comprise water of crystallization in their crystal structures. Thiswater of crystallization reacts with some of the reactive components,such as aluminum chloride. This crystal water is e.g. believed todeactivate aluminum chloride in a preliminary oxidation reaction. Therelease of this water of crystallization is increased during the processof mixing the components together in which mixing process mixingequipment, such as crushers, might be used which generate heat.

When a high grade aluminum chloride is used in the preparation of theRoadCem or Powercem products, this grade is lowered upon storage. Highergrade aluminum chloride is more expensive than lower grade aluminumchloride and when the higher quality does not provide an additionalreactivity since it has deactivated, it is not of any commercial use tostart with a high grade aluminum chloride. With the catalyst and methodof preparation of the additive of the present invention, thisdeactivation does not occur since the catalyst composition in only mixedwith the remaining (water of crystallization containing) components ofthe composition for reinforcing cement shortly before it is used. Inthat case, there is not sufficient time for the deactivation to occurand the higher reactivity of aluminum chloride is maintained. Thetechnical effect, is to supply a highly reactive catalyst compositionfor use in cementing of well bores.

The catalyst composition according to the present invention is preparedand stored separately from the remaining components. Shortly beforeusing RoadCem or PowerCem product of EP 1 349 819 for cementing a wellbore the catalyst composition is mixed with the remaining components.This is hence a novel method of preparing a cement slurry for cementinga wellbore using the composition as disclosed in U.S. Ser. No.13/654,920 and U.S. Ser. No. 13/540,181.

An additional advantage of the present catalytic composition as revealedby research carried out by the present inventors is that it is possibleto use a better grade (higher purity) aluminum chloride, such as 99%(2N), 99.9% (3N), 99.99% (4N) or even 99.999% (5N) Aluminum chloride,without deactivation.

The catalyst composition can be added to cement to increase thereactivity of cement and provide a high energetic value of the cement.Thus the present invention relates to the use of the catalystcomposition to reinforce cement for high-demanding applications, forexample cementing of wellbores.

The catalyst composition of the present invention, viz. the catalystwill in the future probably be marketed by PowerCem Technologies B.V.under the trademark of RC-C (RoadCem-catalyst).

Cement is a salt hydrate consisting of a fine-ground material which,after mixing with water, forms a more or less plastic mass. Cementhardens both under water and in the outside air. Cement is capable ofbonding materials suitable for that purpose to form a mass that isstable also in water. The cement standards according to Europeanstandard NEN-EN-197-1 are as follows: CEM I is Portland cement; CEM IIis composite Portland cement; CEM III is blast furnace slag cement; CEMIV is pozzolan cement and CEM V is composite cement.

Preferred Embodiments of All Aspects of the Present Invention

The present invention is preferably a mixture of noble metals (e.g.aluminum) and non-noble metals (e.g. magnesium) which combined give asynergistic reaction to the formation of stable crystalline structures.

For an optimum composition of the catalyst, the total quantity ofcomponents from group I) may be 1 to 25% by weight, preferably 5 to 15%by weight, more preferably 8 to 13% by weight; most preferably 10 wt. %based on the total weight of I)+II)+III).

For an optimum composition of the catalyst, the total quantity ofcomponents from group II) may be 10 to 50% by weight, preferably 20 to40% by weight, more preferably 25 to 35% by weight, most preferably 30wt. % based on the total weight of I)+II)+III).

For an optimum composition of the catalyst, the total quantity ofcomponents from group III) may be 5 to 40% by weight, preferably 10 to30% by weight, more preferably 15 to 25% by weight, most preferably 20wt. % based on the total weight of I)+II)+III).

Without wishing to be bound to any specific theory, experimental resultsindicate that the components which are present in the catalystcomposition form crystalline structures when added to cement materialwhich are well bonded together and are homogeneously distributed, inbetween the cement particles, and thereby bind the cement particles.Hardened cement which is prepared without this binder or with knownbinders has a relatively open structure when viewed on a microscopicscale, with crystalline agglomerations which are not homogeneouslydistributed. Consequently, the interaction between the crystallineagglomerations and also between the cement particles and the crystallineagglomerations is poor.

The crystalline compounds which are formed by this additive aresurprisingly homogeneously distributed and may be in the form ofacicular (viz. needle-like) structures. The homogeneous distributionresults in an optimum strength and stability. The water in the cement isbound in and to the crystalline structures. Consequently, there are nolocal concentrations of water, and therefore the formation of potentialweak spots is avoided.

The present catalyst composition has been found be induce the forming ofnanoscale crystalline compounds. Hence, the function of the catalyst ofthe present invention is the formation of durable crystal structures.

The catalyst composition according to the present invention can beprepared by combining the required components and dry-mixing them. Thecatalyst composition according to the invention is preferably assembledfrom the abovementioned components in pure form (>97%, or even>98%, oreven>99%).

The sole components of the catalyst composition are ammonium chloride,aluminum chloride, and magnesium oxide. Thus the catalyst composition isconstituted by these three components. No other components are present.One of the uses of the catalyst composition of the present invention isas an (nano-engineered) additive for oil well cementing. The presentcatalyst composition improves flexibility and increases compressivestrength.

One important use of concrete or cement in the oil and gas field is asso-called “well cementing” or the cementing of the drilling or oil well.For this use deep bores are drilled into the ground or soil. The insideof these bores are covered by a metallic layer or pipe that is used toguide the oil from the oil field up to the surface (=casing string).These metallic layers should adhere to surrounding environment (i.e.soil or rock). In order to obtain this adhesion between the metalliclayer (casing or casing string) and the surroundings cement is oftenused.

Wellbores are protected and sealed by cementing, i.e. for shutting offwater penetration into the well, to seal the annulus after a casingstring (viz. a long section of connected oilfield pipe) has beenintroduced down the wellbore, or to plug a wellbore to abandon it.

Cementing is carried out using a cement slurry that is pumped into thewell. In this method, usually the drilling fluids that are presentinside the will are replaced by cement. The cement slurry fills thespace between the casing and the actual wellbore, and hardens to createa seal. This presents external materials entering the well flow andpositioning the casing string into place permanently.

A cement slurry is wet cement obtained by mixing dry cement and waterand optionally one or more additives.

The cement slurry for cementing a wellbore according to the presentinvention, comprises i) cement, ii) water; and iii) a catalystcomposition consisting of I) ammonium chloride, II) aluminum chloride,and III) magnesium oxide.

In an embodiment of the cement slurry, said slurry comprises between 50and 85 wt %, preferably between 65 and 75 wt % of: I) cement, andbetween 20 and 40 wt %, preferably between 25 and 30 wt % of; II) water,and between 0.1 and 10 wt %, preferably between 1 and 3 wt %, morepreferably between 1.5 and 2.5 wt % of composition III).

The wet cement (viz. cement slurry) is obtained by the use of mixers(e.g. hydraulic jet mixers, re-circulating mixers or batch mixers) fromwater and dry cement and one or more additives.

For wellbore cementing Portland cement is most frequently used(calibrated with additives to 8 different API classes). Examples ofadditives are accelerators, which shorten the setting time required forthe cement, as well as retarders, which do the opposite and make thecement setting time longer. In order to decrease or increase the densityof the cement, lightweight and heavyweight additives are added.Additives can be added to transform the compressive strength of thecement, as well as flow properties and dehydration rates. Extenders canbe used to expand the cement in an effort to reduce the cost ofcementing, and antifoam additives can be added to prevent foaming withinthe well. In order to plug lost circulation zones, bridging materialsare added, as well.

A method for well cementing is known in the art. After casing string hasbeen run into the bored well, an cementing head is attached to the topof the wellhead to receive the slurry from the pumps. A so-called bottomplug and top plug are present inside the casing and prevent mixing ofthe drilling fluids from the cement slurry. First, the bottom plug isintroduced into the well, and cement slurry is pumped into the wellbehind it, viz. within the casing and not yet between the casing and itssurroundings. Then the pressure on the cement being pumped into the wellis increased until a diaphragm is broken within the bottom plug,permitting the cement slurry to flow through it and up the outside ofthe casing string, viz. outside of the casing and hence between thecasing and its surroundings. After the proper volume of cement is pumpedinto the well, a top plug is pumped into the casing pushing theremaining slurry through the bottom plug. Once the top plug reaches thebottom plug, the pumps are turned off, and the cement is allowed to set.

Since wellbores are very deep, setting or hardening at deep depths andunder conditions of high temperature and/or high pressure, andoptionally corrosive environments, there are stringent requirements forthe cement.

A few of the challenges today with respect to well cementing arediscussed below.

Despite recent technological advances with elastomers, polymers, fibresand reactive components that self-heal micro fissures, the cement sheathbetween the casing string and the surrounding rock/soil is not alwaysable to deliver an acceptable long-term solution for today's demandingdrilling environment. Changes in down hole conditions with pressure andtemperature fluctuations impose stresses on the cement sheath.Consequently, shrinking and de-bonding of the cement sheath creates verysmall micro cracks allowing fluid migration. Besides these externalforces that cause cement sheath damage an evaluation of conventional oilwell cement sheath on the nanoscopic scale from 1-100 nm reveals thatthe chemical bond between components within the cement itself isrelatively brittle.

Examples of the challenges are: i) micro cracks occurring because offluctuations in pressure and/or temperature inside the well; ii)undesired gas migration due to shrinkage or expansion of the cement;iii) corrosion of the protective casing, which costs hundreds ofmillions and which reduces longevity.

There are several demands required in the field of well cementing, viz.with respect to density, permeability, shrinkage, bonding, chemicalresistance, setting time, viscosity, flexibility, and durability.Moreover, downhole temperature can exceed 200° C.

An example of preferred product criteria for cement for wells are thefollowing:

-   -   Density: value<1300 kg/m³    -   Permeability: material has to be impermeable    -   Shrinkage: material may not shrink, expansion is preferred    -   Bonding: good bond required with steel    -   Chemical resistance: high chemical resistance required    -   Thickening time: materials needs to be workable up to 6 hours    -   Viscosity: preferably 300 CP    -   Flexibility: stretch of 2% without fracturing

Known Portland cement consists of five major compounds and a few minorcompounds. The composition of a typical Portland cement is as follows:50 wt. % of tricalcium silicate (Ca₃SiO₅ or 3CaO.SiO₂); 25 wt. % ofdicalcium silicate (Ca₂SiO₄ or 2CaO.SiO₂); 10 wt. % of tricalciumaluminate (Ca₃Al₄O₆ or 3CaO.Al₂O₃); 10 wt. % of tetracalciumaluminoferrite (Ca₄Al₂Fe₂O₁₀ or 4CaO.Al₂O₃.Fe₂O₃); 5 wt. % of gypsum(CaSO₄.2H₂O)

Without wishing to be bound to any specific theory, experimental resultsdiscussed in prior patent applications of the present inventor U.S. Ser.No. 13/654,920 and U.S. Ser. No. 13/540,181 (both incorporated byreference in its entirety) indicate that the components which arepresent in the composition for reinforcing cement used in the presentapplication form crystalline structures when added to cement materialwhich crystalline structures are well bonded together and arehomogeneously distributed, in between the cement particles, and therebybind the cement particles.

Without wishing to be bound to a theory, the following is observed. Whenwater is added to cement, each of the compounds undergoes hydration andcontributes to the final product. Only the calcium silicates contributeto strength. Tricalcium silicate is responsible for most of the earlystrength during first 7 days. Dicalcium silicate, which reacts moreslowly, contributes only to the strength at later times. Upon theaddition of water, tricalcium silicate rapidly reacts to release calciumions, hydroxide ions, and a large amount of heat. The pH quickly risesover 12 because of the release of alkaline hydroxide (OH—) ions. Thisinitial hydrolysis slows down quickly with a corresponding decrease inheat.

The reaction slowly continues producing calcium and hydroxide ions untilthe system becomes saturated. Once this occurs, the calcium hydroxidestarts to crystallize. Simultaneously, calcium silicate hydrate beginsto form. Ions precipitate out of solution accelerating the reaction oftricalcium silicate to calcium and hydroxide ions, also called LeChatelier's principle. The evolution of heat is then dramaticallyincreased again.

The formation of the calcium hydroxide and calcium silicate hydratecrystals provide “seeds” upon which more calcium silicate hydrate canform. The calcium silicate hydrate crystals grow thicker which makes itmore difficult for water molecules to reach the anhydrate tricalciumsilicate. The speed of the reaction is controlled by the rate at whichwater molecules diffuse through the calcium silicate hydrate coating.This coating thickens over time causing the production of calciumsilicate hydrate to become slower and slower. The majority of space isfilled with calcium silicate hydrate, what is not filled with thehardened hydrate is primarily calcium hydroxide solution. The hydrationwill continue as long as water is present and there are still anhydratecompounds in the cement paste.

Dicalcium silicate also affects the strength of concrete through itshydration. Dicalcium silicate reacts with water in a similar manner astricalcium silicate, but much more slowly. The heat released is lessthan that by the hydration of tricalcium silicate because the dicalciumsilicate is much less reactive. The other major components of Portlandcement, tricalcium aluminate and tetracalcium aluminoferrite also reactwith water. Heat is evolved with cement hydration. This is due to thebreaking and making of chemical bonds during hydration.

The strength of cement bound products is very much dependent upon thehydration reaction just discussed. Water plays a critical role,particularly the amount used. The strength of the product increases,when a lower amount of water is used. The hydration reaction itselfconsumes a specific amount of water. The empty space (porosity) isdetermined by the water to cement ratio. The water to cement ratio isalso called the water to cement factor (abbreviated by wcf) which is theratio of the weight of water to the weight of cement used in the slurry.The wcf has an important influence on the quality of the cementproduced.

Low water to cement ratio leads to high strength but low workability.High water to cement ratio leads to low strength, but good workability.A person skilled in the art of cement is able to determine the optimumwater cement factor based on the component used in the slurry and thepurpose of the cement slurry.

Time is also an important factor in determining product strength. Theproduct hardens as time passes. The hydration reactions get slower andslower as the tricalcium silicate hydrate forms. It takes a great dealof time up to several years for all of the bonds to form, whicheventually determines the product's strength for the life of the well.

When the catalyst composition according to the present invention is usedas additive, moisture remains necessary for hydration and hardening. Thefive major compounds of the hydration process of cement still remain themost important hydration products but the minor products of hydrationprobably change. Furthermore, the rate at which important hydrationreactions occur and the relative distribution of hydration productschanges as a result of the addition of the present inventivecomposition. In addition, the crystallization of calcium hydroxideaccordingly occurs at different rates and the reduction of heatgeneration from the hydration reactions occurs. There are more crystalsformed during the reactions and the relevant crystalline matrix is muchmore extensive.

When adding the present composition, the water changes chemically insphere, electrical load, surface tension and reaches a chemical/physicalequilibrium in the matrix. This complex process depends of the type andmass of materials involved in the cement slurry. Similar to the chemicalprocesses physical aspects are part of the equilibrium process in thematrix when the amount of water, trapped as free water is reduced andthe crystals grow into the empty void space. This makes the product lesspermeable to water and more resistant to all types of attack that areeither water dependant or water influenced. A bigger fraction of thewater is converted to crystalline water than is the case with thereactions in the absence of the present inventive composition. Thereduced porosity and increased crystalline structural matrix increasescompressive, flexural and breaking strength of the product and changethe relative ratio between these strengths.

As before the strength of the product increases when less water is usedto make a product. The hydration reaction itself now tends to consume adifferent amount of water. When the present inventive composition ismixed with oil well cement it is also possible to use salt water andachieve a good end result. According to the best mode of the invention,12.5 kilogram of Dyckerhoff cement API Class G is mixed with 4.75kilogram water and 375 of the catalyst composition, comprising one partammonium chloride to two parts magnesium oxide to three parts aluminumchloride.

Embodiments disclosed in the present invention for one aspect of theinvention are, were applicable, also intended to be used for otheraspects of the inventions, and vice versa. The present invention isfurther explained in the appended claims.

1. Use of a catalyst composition consisting of I) ammonium chloride, II)aluminum chloride, and III) magnesium oxide for addition to cement foroil well cementing.
 2. Composition according to claim 1, wherein thetotal quantity of I) is 1 to 25% by weight, preferably 5 to 15% byweight, more preferably 8 to 13% by weight; based on the total weight ofI)+II)+III).
 3. Composition according to claim 1, wherein the totalquantity of II) is 10 to 50% by weight, preferably 20 to 40% by weight,more preferably 25 to 35% by weight, based on the total weight ofI)+II)+III).
 4. Composition according to claim 1, wherein the totalquantity of III) is 5 to 40% by weight, preferably 10 to 30% by weight,more preferably 15 to 25% by weight, based on the total weight ofI)+II)+III).
 5. Method of cementing a wellbore, comprising the steps of:i) drilling a wellbore; ii) introducing a casing string into thewellbore; iii) preparing a cement slurry based on a combination ofcement and a catalyst composition consisting of a) ammonium chloride, b)aluminum chloride, and c) magnesium oxide; iv) pumping said cementslurry into the wellbore; and v) allowing said cement slurry to set. 6.Cement slurry for cementing a wellbore, comprising i) cement, ii) water;and iii) a catalyst composition consisting of I) ammonium chloride, II)aluminum chloride, and III) magnesium oxide.
 7. Cement slurry accordingto claim 6, comprising between 50 and 85 wt %, preferably between 65 and75 wt % of I) cement, and between 20 and 40 wt %, preferably between 25and 30 wt % of II) water, and between 0.1 and 10 wt %, preferablybetween 1 and 3 wt %, more preferably between 1.5 and 2.5 wt % ofcatalyst composition III).